Porcelain pivot crowns were described in the early
1800s by a well-known dentist of Paris, Dubois de Chemant
One of the best representations of a pivoted tooth appears in Dental Physiology and Surgery , written by Sir John Tomes in 1849 5 Tomes’s post length and diameter conform closely to today’s principles in fabricating posts.
Loss of retention & tooth fracture are the most common causes of post & core failures
Clinical Failure Rate of Posts and Cores Mean values † 6 yr 9 (196 of 2,220 9 (72 of 788) 1–69 mo Torbjörner, 1995 14 (8 of 56) 4–0 y Wallerstedt, 1984 8 (39 of 516) 1–10 y Mentink, 1993 11 (17 of 154) 3 y Hatzikyriakos, 1992 7 (9 of 138) 10 y or more Weine, 1991 9 (9 of 96) 5 y 9 Bergman, 1989 9 (36 of 420) 1–25 y Sorenson, 1984 12 (6 of 52) 5 y Turner, 1982 % Clinical Failure Study Length Lead Author
A parallel post ensures the greatest retention of the post within the canal, and is perhaps utilized with only the slightest loss of tooth structure to the internal wall of the canal.
A smooth-surfaced post, although less retentive than either serrated or threaded post surfaces, transmits the least amount of force to the root structure.
While both smooth and serrated posts are passive, in that they simply lie within the post space after being cemented, threaded posts actively engage the internal walls of the root canal as they are screwed in, and, while being the most retentive by far, produce such a force on the brittle root structure that they are contraindicated in most situations.
The use of a post and core does not strengthen the tooth prior to restoration with a crown; rather, it may contribute to the weakening of the tooth structure, as the forces placed upon the future prosthetic crown and core are now transmitted along virtually the entire length of the brittle, endodontically treated tooth.
Basically, it is important to leave at least 5 mm of gutta percha at the apex of the root canal, because it is within the apical 5 mm of the root canal that 95% of lateral accessory canals split off from the main canal and anastomose with the exterior surface of the root. Should these lateral canals not be blocked with the gutta percha and the cement used to place the gutta percha, the chances of microleakage and percolation of microbes is drastically increased, thereby increasing the likelihood of an endodontic failure . Post apical end